The instant invention relates to an apparatus and method for generating light having a frequency in the range of approximately 250-550 nanometers, and more particularly to such an apparatus and method which utilizes a source of linearly polarized light to generate such light.
There are several applications for use of light having a wavelength in the range of 250-550 nanometers in which the light is used to irradiate a sample in order to determine the presence or absence of a substance in the sample. For example, as described in U.S. Pat. No. 4,446,370, for APPARATUS FOR DETECTING OIL IN WATER by the instant inventor and assigned to the assignee of the instant application, ultraviolet light may be shined into a portion of the water while monitoring for fluorescence which indicates the presence of oil. Likewise, ultraviolet light is used to irradiate core samples taken from a well bore in order to determine whether oil may be present in the sample. Alternatively, instead of removing the sample from the well bore, a source of ultraviolet light may be lowered into the bore for irradiating subsurface formations at different levels.
In each of the above applications, it may be necessary to provide a light source at relatively inaccessible locations, e.g., submerged in a body of water or lowered into a well bore. It has been found in the past that using optical fibers for transmission of ultraviolet light is not effective due to attenuation by the fibers of light in the ultraviolet range.
It is a general object of the present invention to provide a source of light having a wavelength in the range of 250-550 nanometers at a location remote from a linearly polarized light source, the light of which is used to generate such remote light.
It is a more specific object of the invention to provide such a method and apparatus which utilizes optical fibers to transmit the linearly polarized light at its optimum frequency for fiber transmission.
The apparatus includes a source of linearly polarized light and an optical fiber for transmitting such light therealong. A frequency-doubling crystal is positioned adjacent one end of the fiber so that such transmitted light passes therethrough. The transmitted light is selected from substantially the 500 to 1100 nanometer wavelength range which is optimum for transmission along optical fibers. The transmitted light which emerges from the crystal includes light in the 250-550 nanometer range, such light being twice the frequency of the transmitted light. A frequency-mixing crystal may be used in lieu of the frequency-doubling crystal to obtain further variation in the wavelength of the produced light.